Crowd scenes have always been a major challenge for film directors and a source of concern for producers. In the good old days of silent movies, when a scene required 5,000 extras, well, one just had to hire 5,000 extras. By using prism lenses, a gifted cinematographer could create the illusion of an even larger crowd. With the development of optical compositing, directors managed to achieve the effect in a much more convincing way. A crowd of 1,000 could be created on film by combining five plates of 200 extras.

For several decades, optical crowd duplication would remain the only technique that allowed very large numbers of people to appear on screen besides matte painting for static crowds. One notable exception is Gandhi (1982): for the funeral scene of the title character, almost 100,000 Indian extras were hired (at the local rate), but 200,000 more showed up on the filming location for free! As a result, the scene now boasts what is probably the largest real crowd ever shown on film.

With the advent of computer generated extras, film directors discovered that they could direct a virtual crowd just as they would with real people on a movie set. Major productions such as Titanic, Star Wars: Episode I and The Grinch pioneered the effect. Everyones game was raised with the release of The Lord of the Rings trilogy. For this production, Weta Digitals engineers developed a revolutionary software that allowed each digital extra to basically decide on its own what it should be doing. Dubbed Massive, this new technology allowed the creation of the most impressive battle scenes ever put on film.

Framestore CFC was assigned the task of creating the Greek armada. There are only two real ships in this shot; the rest are digital.

The Mother of All Battles

When Warner Bros.Troy went into production, it was clear for all involved that their battles had to surpass these landmark scenes. After all, their movie was based on the greatest battle of all times. Overall visual effects supervisor Nick Davis assigned the ambitious sequences to London-based The Moving Picture Co. We did about 425 shots, all focused on the battle scenes and the creation of the city of Troy, explains Chas Jarrett, MPCs visual effects supervisor. We started in November 2002 with six months of research and development led by Julian Mann, our R&D supervisor. We knew that crowd simulation technology would be paramount to the success of the battle scenes. Our first option was to simply buy Massive licenses. However, we found out that the software was a simplified version of the program that had been used on the Peter Jackson movies. It didnt have all the functions that we needed. Plus, it was pretty costly: at $40,000 per license, it was three times more expensive than your regular Maya license. And we needed 20 of them

Eventually, Jarrett and Mann realized that they had no other choice but to develop their own crowd simulation software utilizing CG animation and artificial intelligence. A team of 10 programmers worked full-time on the project for 15 months, ultimately producing some 40 different applications combined into one user-friendly program. Two major components of the software were the motion capture database, dubbed Emily (for M.L.E.: Motion Library Editor), and the animation program, dubbed Alice. There were two steps in creating and animating a CG soldier, explains Jarrett. First, we gave him senses: he was able to see, hear, feel the ground under his feet, make the difference between an enemy and a fellow soldier. Then, we told him what to do with this information.

MPC developed two software components, Emily and Alice, that were used to create the digital soldiers. Here, Agamemnon's army marches outside the city of Troy.

The process started with three weeks of motion capture covering 90 different moves. The actors randomly performed these moves for two minutes at a time. The data was then broken by Emily into eight-frame segments, which created a motion library of some 1,000 clips. Once the database was completed, the program analyzed each individual clip and referenced all the other clips that it could be blended with. In the end, the 1,000 clips were able to produce 100,000 different combinations, thus giving the effects team a virtually unlimited variety of movements.

The idea was that any single motion, such as walking or running, would be the result of, say, 100 different moves combined together, comments Jarrett. Our A.I. program would say: I want this individual to walk from A to B, and Emily would answer: Here is what I have. Select the walk clips that you need. It meant that you could never have two characters walking or running the same way since the clips combination would always be different.

CG soldiers were sometimes placed next to real soldiers in group battle scenes, such as this one where Greek warriors meet face to face against the Trojan soldiers outside the walls of Troy.

Making it Look Good

Although Alice was designed to handle thousands of CG extras, the animators could isolate groups of soldiers, or even individuals, and modify or delete specific action. During the animation process, the characters were represented as mere squeletons, even as cube piles some times. The actual geometry was added in the shader, a task handled by CG supervisor Gary Brozenich and his team. Depending on the nature of the scene, the number of CG soldiers would vary from shot to shot. In theory, there were 50,000 Greeks against 25,000 Trojans, notes Jarrett. However, there were shots in which it looked like there was much less than 75,000 soldiers on screen. So, we decided to handle it on a shot per shot basis, adding as many soldiers in the frame as needed to make it look good. With this approach, we ended up with shots featuring 150,000 soldiers!

The A.I. program produced realistic crowd animations, but was not suited for complex combat simulation. Individual fights were handled separately, with stuntmen performing complicated routines on a MoCap stage. The resulting animation was composited in the foreground of the battle scenes by digital effects supervisor Rudi Holzapfels team. As often is the case, CG soldiers ended up much closer to camera that what had originally been planned. The CG extras had been developped for long shots, but eventually, we had to use them in closeups too adds Jarrett. There are some shots in which CG soldiers are composited right next to the principal actors.

As if the massive shots on the battling armies were not enough, MPC also created many effects involving the main characters in action. Brad Pitt, Orlando Bloom and company didnt exactly shout it out in the media, but many of their action shots were filmed without an actual weapon in sight To start with, Bloom never fired one single arrow on the set, although his character Paris is a gifted archer in the film. He made the move of firing, empty-handed, and we added the arrows in CG, reveals Jarrett. The same was done on the swords. It was too dangerous for the principals to swing their weapon on the set. So, they only had the handle and the blade was added in CG. In some shots, we also had to replace their hand, or even the whole arm, with a digital replica in order to animate a more natural move its difficult to simulate the action of hitting something when you actually dont hit anything.

Besides the battle scenes, MPC also tackled the creation of the city itself. For a while, Jarrett considered using a large miniature but eventually opted for a complete CG approach after watching a test in which a virtual building proved to be as realistic as its model counterpart. 30 buildings were modeled in CG, each side featuring different details in order to multiply the possibilities. Another layer of variety was added with color patterns and some 25GB of textures.

MPC modeled 30 buildings in CG to create the city of Troy.

The Mighty Fleet

With MPC deep immersed into epic battles and antique cities, the task of recreating the allied armada and its landing was assigned to Framestore CFC, London. The 130 shots were supervised by Jon Thum: The pullback on the armada at sea was our most difficult shot. There are only two real ships in the shot, the rest is completely digital. We built them as modular creations, each model combining elements taken among five different hulls, five prows, and about one hundred sails. By combining these elements, we managed to create a whole armada in which every ship looked different. At the end of the shot, there are about 800 ships in the frame. If you count in the units that are out of frame, you get an armada of 1,000 ships.

The most difficult aspect of the shot was not the creation of the fleet itself, but the tracking that allowed it to be anchored to the surface of the sea. In order to track an element into a shot, you need to have stable reference points in the frame, explains Thum. However, when youre out at sea, there are no such things as stable tracking marks. What we came up with was to shoot the plates with two dinghies pulling five buoys evenly spaced on a 80-yard rope alongside the hero ships. It gave us the reference we needed and allowed us to track the shot, at least most of it at the end of the move, the camera was one mile away from the ships, which meant that we could no longer see our buoys. It took a lot of finessing to get the tracking right. In the end, this one shot was several months in the making

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The landing on the beach presented its own set of problems. Framestore CFC had to add 4,000 digital soldiers to the 400 extras that had been photographed, plus hundreds of ships at sea. The CG army was created via motion capture with actors performing a great variety of actions: carrying, digging, pulling, etc. The hero shot of the landing sequence is a helicopter flyover of the whole beach. This shot was 30 seconds long and showed just everything. To make things more complicated, the operator had tilted up too early and as a result, there was no real extra on the beach at the beginning of the plate: they were all gathered at the other end. It meant we had to work with an empty beach for most of the shot Without any reference in the plate, it made the whole process very difficult.

To complete the work done at MPC and Framestore CFC, 165 shots were assigned to Cinesite Europe, London. Supervised by Sue Rowe, the effects included a rain of digital flaming arrows on the Greek soldiers, the duplication of fireball elements launched by the Trojan army and the addition of a CG blade on Pitts weapon in the beach battle.

Whats Next?

With their sweeping camera moves and intricate action, the Troy crowd scenes clearly mark another improvement in the field. In fact, one may wonder what the next step could be. The digital extras in Return of the King and Troy already are full frame, in bright sunlight, in shots lasting several seconds. Where do we go from there? We may very well have to wait for the release of Star Wars: Episode III to get an answer to that question

Alain Bielik is the founder and special effects editor of renowned effects magazine S.F.X, published in France since 1991. He also contributes to various French publications and occasionally to Cinefex.